1. Field of the Invention
The present invention generally relates to a linear guiding apparatus for a machine tool. More specifically, the invention relates to a linear guiding apparatus for guiding a feed motion of a movable body, such as a table of a machine tool, which is provided with a hybrid guide system such as a combination of a sliding guide and a rolling guide.
2. Description of Related Art
In machine tools, a linear guide for movable bodies, such as columns, spindle heads and tables, are generally classified under two categories, i.e., a sliding guide and a rolling guide. The sliding guide is in sliding contact with a guide way and acts as a damper element which absorbs kinetic energy of the movable body in consequence of kinetic friction. It is possible for the sliding guide to acquire damping characteristics of vibration which is the cause of high frequency vibration of the movable body. The rolling guide is in rolling contact with a guide way and does not act as a damper element, but the rolling guide possesses an advantage of reduced kinetic friction and is suitable for high speed feed motion.
Conventionally, the sliding guides are mainly used for movable bodies in machine tools. However, in recent years, rolling guides are widely current in the field of machine tools. Moreover, a hybrid type guiding system which is a combination of a sliding guide and a rolling guide has been developed. The hybrid type guiding system can change into the sliding guide so as to require damping characteristics in the case of a heavy cutting with a reduced speed feed motion. In the case of a high speed feed motion, the hybrid type guiding system can change into the rolling guide. Therefore, the hybrid type guiding system can enjoy advantages of both the sliding guide and the rolling guide. Such conventional hybrid type guiding systems are disclosed, for example, in Japanese Patent Laid-Open Nos. 1998-131634 and 2001-9655.
However, there are disadvantages common to conventional hybrid type guiding systems in that the hydraulic pressure control for obtaining required damping characteristics is complicated since the load of a movable body has a great influence on the damping characteristics of the sliding guide.
In addition, in the guiding system disclosed in Japanese Patent Laid-Open No. 1998-131634, a hydraulic cylinder is provided between a rolling guide and a movable body so as to be capable of changing a share of contribution by the sliding guide or the rolling guide. In a case where the rolling guide takes a large share of the guiding function to extend the stroke of the hydraulic cylinder, the moment rigidity of the hydraulic cylinder decreases, so that the rigidity between the movable body and the rolling guide decreases, thereby decreasing the precision of movement during a high speed feed motion. Similarly, in the guiding system disclosed in Japanese Patent Laid-Open No. 2001-9655, a rolling element of a rolling guide is provided between a guide rail and a sliding surface of a slider, and a hydraulic cylinder presses a brake shoe against the guide rail to increase its braking force to obtain damping characteristics. The deterioration of the precision of the guide rail cause by the friction of the brake shoe inevitably follow the deterioration of the precision of movement.
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a linear guiding apparatus for a machine tool, which achieves both of the rolling guide with high speed feed ability without deteriorating the precision of movement and a sliding guide with damping characteristics without being influenced by the load of a movable body.
In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, there is provided a linear guiding apparatus combining a rolling guide with a sliding guide for guiding the movement of a movable body on a bed of a machine tool, said apparatus comprising a rolling guide means configured to guide the movable body in the horizontal direction while supporting a load of the movable body on the bed, a sliding guide means having a sliding guide way extending in parallel to the rolling guide means and the vertical plane, and a slider member having a slide plate configured to slide on the sliding guide way; and frictional force generating means configured to press the slide plate against the sliding guide way.
According to this linear guiding apparatus, the load of the movable body is not applied to the sliding guide way, so that it is possible to add damping characteristics to the sliding guide without being influence by the load, thereby coping with both the rolling guide and the sliding guide.
In the above described linear guiding apparatus, the frictional force generating means may be build in the slider member, and comprises an actuator for pressing the sliding plate against the sliding guide way, and control means for controlling a pressing force of the actuator.
According to this linear guiding apparatus, when a heavy cutting feed is carried out, the pressing force of the actuator can be increased to enhance the damping characteristics of the sliding guide way, and when a rapid feed or a light cutting feed is carried out, the pressing force can be decreased to reduce the influence of the sliding guide way to carry out a guide suitable for the rapid feed.
In the above described feed guiding system, said sliding guide means may be provided with sliding guide ways formed on both sides of the bed so as to be perpendicular to a movable body mounting surface on the bed, and a pair of sliding members mounted on the both side of the movable body, each of said sliding member having the sliding plate configured to slide on the sliding guide ways.
According to this linear guiding apparatus, nothing is provided between the movable body and the rolling guide, so that it is possible to cope with both the rolling guide and the sliding guide without deteriorating the precision of movement of the rolling guide.